This application claims the priority of 198 31 251.2-13, filed Jul. 11, 1998, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a superchargeable internal combustion engine with cylinder cut-off, in which a first cylinder group operates over the entire operating range of the internal combustion engine and a second cylinder group can be connected up as required.
In order to reduce the fuel consumption, particularly in powerful internal combustion engines of commercial vehicles, these internal combustion engines can be equipped with cylinder cut-off. One group of cylinders can be connected up or cut off as a function of the output. Inasmuch as modern internal combustion engines are also optimized with respect to their pollutant emissions such that they have minimum emission values in a relatively high load range, the cylinder cut-off is also used for pollutant reduction because the cut-off cylinders do not produce any pollutants. As a result of the cut-off, the cylinders which are not cut off are more severely loaded and are able to operate in the optimized-emission high load range. In these internal combustion engines as disclosed for example, in DE 33 09 434 C1, only some of the cylinders are then involved in the development of the output, for example when starting or during idling and during part-load operation.
In addition, DE 36 33 405 A1 discloses an internal combustion engine of the above-mentioned type which has a first cylinder group which operates over the entire operating range of the internal combustion engine, and a second cylinder group which is cut off in part-load ranges and can be connected up as required, a separate exhaust-gas turbocharger additionally being assigned to each cylinder group in order to increase the output of the internal combustion engine. The turbocharger assigned to the first cylinder group is driven by the exhaust gases of the first cylinder group, while the other turbocharger serving to supercharge the second cylinder group is driven by the exhaust gases of the second cylinder group.
At a transition from part-load operation, in which the second cylinder group is cut off, to full-load operation, in which all the cylinders of the known internal combustion engine operate, the cylinders of the second cylinder group initially require a start-up phase, during which the associated exhaust-gas turbocharger also begins operation. Because the turbines of the exhaust-gas turbocharger can develop their output only above a specific flow velocity, the increase in output as a result of the supercharging of the charging air for the second cylinder group begins only after a noticeable time delay. An internal combustion engine of this type, which is supercharged by two exhaust-gas turbochargers, therefore has a sluggish response when the second cylinder group is connected up.